Pentafluorosulfur hypofluorite, SF.sub.5 OF, is disclosed by Williamson et al., Inorganic Chemistry, Vol. 1, pp. 673-677 (1962). Williamson et al. disclose that SF.sub.5 OF does not react with CO at room temperature but that these materials do react when temperature is raised to 165.degree.C. The disclosed products of this reaction are carbonyl fluoride, F.sub.2 CO, and thionyl tetrafluoride, SOF.sub.4.